How long do MRE stay good for?
Where can I find MRE's at a resonable price?
How long do MRE stay good for?
It really depends on what's in the MRE. The average time is 4 years if stored at 60 degrees. There are much, much better alternatives to long term food storage both in terms of longevity and overall cost. Try the Augason Farms line from Sam's (online only, at least in Baton Rouge) or the Mountain House stuff they package in #10 cans (you can find them on Amazon). Freeze dried food lasts much longer than other means of preserving. The old MRE's used to have freeze dried food in them. I do not believe they do any more.
The following link can shed some more light on MRE shelf life:
http://www.mreinfo.com/us/mre/mre-shelf-life.html
If you're still set on buying MRE's then there's a link on the sidebar of that page where you can purchase the civilian versions. Be warned that rats and mice can and will find your stash of MRE's if you don't protect them well.